234 STATISTICS OF WHEAT CULTURE. 



I have adopted is, to say the least, as free from objection as any other, and if 

 carefully and uniformly carried out, will truly represent the relative values of 

 the several samples of wheat flour. As this is a matter of much consequence in 

 a practical point of view, I trust I shall be excused for introducing some addi- 

 tional facts in regard to it. 



The term r/luten was originally applied to the gray, viscid, tenacious, and 

 clastic matter, which is obtained by subjecting wheat flour to the continuous 

 action of a current of water. But it appears that this is a mixture of fibrinc and 

 caseine, with what is now called glutine, and a peculiar oily or fatty matter. 

 Now these substances may be separated from each other, but the processes em- 

 ployed for this purpose are tedious, and to insure accuracy the various solvents 

 must bo entirely pure a point which, especially in the case of alcohol and ether, 

 is not ordinarily easy to be attained. This will be rendered still more evident 

 by a reference to a French process, which will hereafter be noticed. 



But were it much less difficult in every case accurately to separate the con- 

 stituents of gluten, it would not, in my opinion, be of the least practical utility. 

 It is to the peculiar mechanical property of this gluten that wheat flour owes 

 its superior power of detaining the carbonic acid engendered by fermentation, 

 and thus communicating to it the vesicular spongy structure so characteristic of 

 good bread.* It may also be adde<i, that the results of more than one hundred 

 trials have satisfied me that a diminution or loss of elasticity in the gluten is the 

 surest index of the amount of injury which the sample of flour has sustained. 

 Whether, therefore, the sample contains a certain proportion of nitrogen, or 

 whether it contains albumen, fibrine, and caseine in sufficient quantity, it may 

 still want the very condition which is essential to the manufacture of good 

 bread. My objection, therefore, to the mere determination, however accurate, 

 of the proportion of nitrogen contained in wheat flour, or of the various princi- 

 ples which form the gluten, is, that it does not represent the value of the various 

 samples for the only use to which they are applied, viz., the making of bread. 

 The remarks of Mulder, the celebrated Dutch chemist, upon the subject of ma- 

 nures, are so applicable to this point that I cannot refrain from quoting them. 

 " It has," he says, " become almost a regular custom to determine the value of 

 manures by the quantity of nitrogen they yield by ultimate analysis. This 

 method is entirely erroneous ; for it is based upon the false principle, that by 

 putrefaction all nitrogcneous substances are immediately converted into am- 

 monia, carbonic acid, and water ! But these changes sometimes require amimber 

 of years. Morphine, for example, is prepared by allowing opium to putrefy ; 

 and the process for preparing leucin, a substance which contains 10. 72 of nitrogen, 

 is to bring cheese into putrefaction. Cheese, therefore, does not perhaps in a 

 number of years resolve itself into carbonic acid, ammonia, and water, but pro- 

 duces a crystalline substance, which contains no ammonia. Hence the proportion 

 of nitrogen yielded by manures is not a proper measure of their value, and there- 

 fore this mode of estimating that value ought to be discontinued."t 



We infer, therefore, that tke proportion of nitrogen furnished by food of 

 various kinds is not the true measure of their nutritious value, and cannot for 

 practical purposes take the place of that process by which the amount of rough 

 gluten is determined. 



No better illustration can be given of the uncertainty which attends the in- 

 ferences drawn from the ultimate composition, than the fact heretofore stated in 

 regard to hay, the nutritive value of which is placed in the tables containing the 

 results of these analyses, at a figure nearly the same as that of ordinary wheat 

 flour. { 



In the paper on the " Composition of Wheat," by M. Peligot (" Comptes 

 Rendus," February 5th, 1849) to which I have already referred, the author gives 

 tho results of the various analyses which he has made, and details the process 

 ho adopted. 



Aware of the complex and difficult nature of the examination as conducted 

 by hiru, he seems to doubt in regard to some of the results given in his tables _ 



Experimental Researches on the Food of Animals, &c., by It. D. Thomson, M.D. p. 156. 

 t Chemistry of Vegetable and Animal Physiology, translated by Prof. J. F.'W. Johnston, 



$ See Dr. R. D. Thomson's Experimental Researches on the Food of Animals, &c. 



